The present invention generally relates to relays that provide protective control of power distribution systems. More particularly, the present invention relates to a technique for synchronizing the gathering of fault data from multiple protective relays.
Power system faults can start and finish rapidly. Protective relays are designed to sense faults and provide protective control by operating a circuit breaker to interrupt the fault. A modem protective relay incorporates digital signal processing to analyze fault data by capturing sampled waveforms before and after the protective relay interrupts the power system. To fully analyze the cause and extent of a fault, analysis of fault data at multiple locations on the power system is necessary.
Conventional systems for monitoring protective relay fault data are primarily master-slave communication systems in which a central control station (master) initiates communications to the protective relays (slaves). In master-slave systems, the master initiates all communications. In a common approach, the master control station cyclically and sequentially monitors each slave device for a change of state. This monitoring process introduces significant delays between the time that the relay reacts to a fault and the control station learns of the fault. The control station can signal other relays to record a waveform, but the ensuing delay is unacceptable in master-slave systems for capturing information at the time of the fault across the system.
U.S. Pat. Nos. 5,224,054 and 5,233,538 to Wallis disclose the capturing of synchronized sampled data in master-slave systems. These patents disclose a technique which employs a control station which sends a command signal to multiple xe2x80x9ccircuit monitorsxe2x80x9d to synchronously sample the system at the present or a future time. While this approach is adequate for characterizing a power system on demand or at a scheduled time, this approach does not adequately address the synchronization of fault data because faults do not occur according to a schedule.
Current advanced trip units and protective relays capture waveforms at the time of the fault. In a typical arrangement, a protective relay will continuously measure and discard up to 72 cycles of power system data. When the (unexpected) fault occurs, the protective relay continues to sample the waveform (and other calculated parameters and status flags) for a preset number of cycles. After this period, the full number of stored samples, comprising cycles of power system information before and after the fault are place in storage for future communication to a local or remote computer. While this process effectively provides fault data information, it does so at only one point in the system.
In view of the above discussion, it would be desirable to provide a method for synchronously recording sampled power system data at multiple points in the power system when a power system event occurs. It would further be desirable for such data to be post-processed to synchronize the information from multiple sources.
In accordance with the exemplary embodiments described below, the present invention can be implemented by sensing a power system event, such as a fault, in a first protective relay associated with a first point on the power system; recording a time tag of the power system event and a first set of power system data; and transmitting a data message from the first protective relay to remote protective relays over a peer-to-peer communications network. The first protective relays and remote protective relays are preferably synchronized (e.g., by a common time standard), The data message preferably includes the time tag of the power system event. Each remote relay can then use the time tag to save its own set of power system data which is synchronized to the first set of power system data.
The technique of the present invention advantageously provides system-wide data surrounding a fault, power surge, or other power system event. This information permits a user to analyze more accurately the cause and effects of the power system event.